JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
  <div></div>
  <li id="foo1">foo</li>
  <li id="bar1">bar</li>
  <li id="baz1">baz</li>
  <div></div>
</ul>

CSS

ul li{color:red}

JavaScript

var $foo = $('#foo1');
console.log('Index: ' + $foo.index()); // 1

var $listItem = $('li');
// this implicitly calls .last()
console.log('Index: ' + $listItem.index()); // 3
console.log('Index: ' + $listItem.last().index()); // 3

var $div = $('div');

// this implicitly calls .last()
console.log('Index: ' + $div.index());  // 4
console.log('Index: ' + $div.last().index()); // 4